That's a great question! I'm afraid I don't know of any specific examples of that we have on record, but in general I wonder how true it is. Certainly there were many people who did not know Latin, but two different contexts come to mind: on one hand, a church in a city or court chapel attended by nobility, other clergy, etc.; on the other hand, a rural parish attended by the local townspeople and farmers. At the former, the priest shouldn't be able to get away with that, because it's the other priests and sometimes the nobility who'd have access to that kind of education. In the former, many parish priests were not much more educated than their parishioners - over in Germany, when Martin Luther and his compatriots went around to these kinds of churches in the 1520s, he was shocked at how theologically ignorant many priests were. It's possible some of them didn't know Latin either; they just memorized the words of the mass.

Laity unfamiliar with Latin is the source of one modern phrase: "hocus pocus," which likely derives from "hoc est corpus meum," "this is my body" in the consecration of the Eucharist. That stems from the misunderstanding of Latin, but from hearing the priest actually using the right words.

So of course I can't say it never happened, and I'd be interested to hear any examples if they exist, but my instinct is that it would be somewhat rare to find a priest with sufficient education to do that yet not be in a place with no risk of being understood. That's at public mass, though - private masses are a different story altogether. Private masses, said by a single priest at an altar with no congregation, were big business because the wealthy would leave large endowments to pray for themselves and their families; the basic idea was to help them out of purgatory sooner.

These private masses, being private, were open to all kinds of shortcuts - there are records of priests speeding through them to get through more in a faster time, leaving parts out, and in at least one recollection, mocking the mass itself: "bread you are and bread you will remain" instead of "this is the body of Christ."

So what your teacher describes, I am somewhat skeptical would happen in public worship, but very much could believe it in a private mass.